High octane gasoline is required for modern gasoline engines. Formerly it was common to accomplish octane number improvement by the use of various lead-containing additives. When lead was phased out of gasoline for environmental reasons, became necessary to rearrange the structure of the hydrocarbons used in gasoline blending in order achieve higher octane ratings. Catalytic reforming is a widely used process for this refining of crude oil to increase the yield of higher octane gasoline which sells at higher prices. The traditional gasoline blending pool normally includes C4 and heavier hydrocarbons having boiling points of less than 205° C. (395° F.) at atmospheric pressure. In catalytic reforming, the paraffins and naphthenes are passed through the reformer with the goal of minimizing cracking. Instead their structure is rearranged to form higher octane aromatics. Essentially catalytic reforming converts low octane paraffins to naphthenes. Naphthenes are converted to higher octane aromatics. Aromatics are left essentially unchanged.
The chemical reactions involved in a reforming process are very complex. The reactions are commonly grouped into four categories: cracking, dehydrocyclization, dehydrogenation, and isomerization. A particular hydrocarbon/naphtha feed molecule may undergo more than one category of reaction and/or may form more than one product.
Catalytic reforming processes are catalyzed by either mono-functional or bi-functional reforming catalysts. A mono-functional metallic catalyst usually has only one (precious) metal catalytic site for catalyzing the reforming reactions. Also known are bimetallic functional catalyst in which two different precious metals exist to provide two metallic catalytic sites. A bi-functional catalyst has both metal sites and acidic sites. Refineries generally use a platinum catalyst or platinum alloy supported on a silica or silica-aluminum substrate as the reforming catalyst, although other catalysts, including the oxides of aluminum, chromium, molybdenum, cobalt, and silicon can be used.
The selection and/or design of a particular reforming catalyst primarily depends on the hydrocarbon/naphtha feed composition, the impurities present therein, and the desired products. A catalyst can be designed, or may be selected, to favor one or more of the four categories of chemical reactions, and thereby may influence both the yield of and selectivity of conversion of paraffinic and naphthenic hydrocarbon precursors to particular aromatic hydrocarbon structures. Efforts continue to advancing reforming technology, especially with the ever-changing demands for gasoline.
Currently, refiners are limiting the quantity of benzene that is blended into the gasoline pool. Benzene is one of the products of the reforming process. Described herein is a process for efficiently removing the benzene from the reforming reactor effluent, concentrating the benzene, and saturating the benzene.